Internal combustion engines frequently misfire on one or more cylinders, requiring repair to that cylinder or cylinders. In order to diagnose such engines, one must determine which cylinder is encountering a problem. The diagnostics typically involve disabling a cylinder and then monitoring the resulting engine performance. Each cylinder is evaluated to determine which cylinder or cylinders is encountering a problem. In general, if a properly operating cylinder is disabled, the engine will run rougher. Conversely, if a non-properly operating cylinder is disabled, there will be little impact on the performance of the engine. By systematically disabling the cylinders of the engine one at a time, one can locate the defective cylinder.
A variety of techniques for disabling a cylinder are known, such as that described in U.S. Pat. No. 4,027,532 (the '532 patent). There are disadvantages to these prior systems. One such disadvantage is that they are difficult to connect to the engine. In today's engines, the component parts are less accessible and are often hidden under plastic cladding. So, attaching all the necessary leads to disable a cylinder is a daunting task. In FIG. 1 of the '532 patent, several different leads are required to perform the test. In today's engine, most of those engine components are inaccessible.
Therefore, improvements are desirable.